4 #include <avr/interrupt.h>
9 // Limits the amount of we wait for any one i2c transaction.
10 // Since were running SCL line 100kHz (=> 10μs/bit), and each transactions is
11 // 9 bits, a single transaction will take around 90μs to complete.
13 // (F_CPU/SCL_CLOCK) => # of μC cycles to transfer a bit
14 // poll loop takes at least 8 clock cycles to execute
15 #define I2C_LOOP_TIMEOUT (9+1)*(F_CPU/SCL_CLOCK)/8
17 #define BUFFER_POS_INC() (slave_buffer_pos = (slave_buffer_pos+1)%SLAVE_BUFFER_SIZE)
19 volatile uint8_t i2c_slave_buffer[SLAVE_BUFFER_SIZE];
21 static volatile uint8_t slave_buffer_pos;
22 static volatile bool slave_has_register_set = false;
24 // Wait for an i2c operation to finish
26 void i2c_delay(void) {
28 while(!(TWCR & (1<<TWINT)) && lim < I2C_LOOP_TIMEOUT)
31 // easier way, but will wait slightly longer
35 // Setup twi to run at 100kHz
36 void i2c_master_init(void) {
39 // Set TWI clock frequency to SCL_CLOCK. Need TWBR>10.
40 // Check datasheets for more info.
41 TWBR = ((F_CPU/SCL_CLOCK)-16)/2;
44 // Start a transaction with the given i2c slave address. The direction of the
45 // transfer is set with I2C_READ and I2C_WRITE.
46 // returns: 0 => success
48 uint8_t i2c_master_start(uint8_t address) {
49 TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTA);
53 // check that we started successfully
54 if ( (TW_STATUS != TW_START) && (TW_STATUS != TW_REP_START))
58 TWCR = (1<<TWINT) | (1<<TWEN);
62 if ( (TW_STATUS != TW_MT_SLA_ACK) && (TW_STATUS != TW_MR_SLA_ACK) )
63 return 1; // slave did not acknowledge
69 // Finish the i2c transaction.
70 void i2c_master_stop(void) {
71 TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
74 while(!(TWCR & (1<<TWSTO)) && lim < I2C_LOOP_TIMEOUT)
78 // Write one byte to the i2c slave.
79 // returns 0 => slave ACK
81 uint8_t i2c_master_write(uint8_t data) {
83 TWCR = (1<<TWINT) | (1<<TWEN);
87 // check if the slave acknowledged us
88 return (TW_STATUS == TW_MT_DATA_ACK) ? 0 : 1;
91 // Read one byte from the i2c slave. If ack=1 the slave is acknowledged,
92 // if ack=0 the acknowledge bit is not set.
93 // returns: byte read from i2c device
94 uint8_t i2c_master_read(int ack) {
95 TWCR = (1<<TWINT) | (1<<TWEN) | (ack<<TWEA);
101 void i2c_reset_state(void) {
105 void i2c_slave_init(uint8_t address) {
106 TWAR = address << 0; // slave i2c address
108 // TWEA - enable address acknowledgement
109 // TWINT - twi interrupt flag
110 // TWIE - enable the twi interrupt
111 TWCR = (1<<TWIE) | (1<<TWEA) | (1<<TWINT) | (1<<TWEN);
120 // this device has been addressed as a slave receiver
121 slave_has_register_set = false;
125 // this device has received data as a slave receiver
126 // The first byte that we receive in this transaction sets the location
127 // of the read/write location of the slaves memory that it exposes over
128 // i2c. After that, bytes will be written at slave_buffer_pos, incrementing
129 // slave_buffer_pos after each write.
130 if(!slave_has_register_set) {
131 slave_buffer_pos = TWDR;
132 // don't acknowledge the master if this memory loctaion is out of bounds
133 if ( slave_buffer_pos >= SLAVE_BUFFER_SIZE ) {
135 slave_buffer_pos = 0;
137 slave_has_register_set = true;
139 i2c_slave_buffer[slave_buffer_pos] = TWDR;
146 // master has addressed this device as a slave transmitter and is
148 TWDR = i2c_slave_buffer[slave_buffer_pos];
152 case TW_BUS_ERROR: // something went wrong, reset twi state
157 // Reset everything, so we are ready for the next TWI interrupt
158 TWCR |= (1<<TWIE) | (1<<TWINT) | (ack<<TWEA) | (1<<TWEN);